linux-kernel - Re: [PATCH] f2fs: multidev: fix to recognize valid zero block address

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Date: Tue, 26 Mar 2024 21:26:28 +0800
From: Yi Zhang <yi.zhang@...hat.com>
To: Chao Yu <chao@...nel.org>
Cc: jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net, 
	linux-kernel@...r.kernel.org, 
	"Shin'ichiro Kawasaki" <shinichiro.kawasaki@....com>
Subject: Re: [PATCH] f2fs: multidev: fix to recognize valid zero block address

I confirmed the issue was fixed now, thanks.

Tested-by: Yi Zhang <yi.zhang@...hat.com>

On Mon, Mar 25, 2024 at 11:26 PM Chao Yu <chao@...nel.org> wrote:
>
> As reported by Yi Zhang in mailing list [1], kernel warning was catched
> during zbd/010 test as below:
>
> ./check zbd/010
> zbd/010 (test gap zone support with F2FS)                    [failed]
>     runtime    ...  3.752s
>     something found in dmesg:
>     [ 4378.146781] run blktests zbd/010 at 2024-02-18 11:31:13
>     [ 4378.192349] null_blk: module loaded
>     [ 4378.209860] null_blk: disk nullb0 created
>     [ 4378.413285] scsi_debug:sdebug_driver_probe: scsi_debug: trim
> poll_queues to 0. poll_q/nr_hw = (0/1)
>     [ 4378.422334] scsi host15: scsi_debug: version 0191 [20210520]
>                      dev_size_mb=1024, opts=0x0, submit_queues=1, statistics=0
>     [ 4378.434922] scsi 15:0:0:0: Direct-Access-ZBC Linux
> scsi_debug       0191 PQ: 0 ANSI: 7
>     [ 4378.443343] scsi 15:0:0:0: Power-on or device reset occurred
>     [ 4378.449371] sd 15:0:0:0: Attached scsi generic sg5 type 20
>     [ 4378.449418] sd 15:0:0:0: [sdf] Host-managed zoned block device
>     ...
>     (See '/mnt/tests/gitlab.com/api/v4/projects/19168116/repository/archive.zip/storage/blktests/blk/blktests/results/nodev/zbd/010.dmesg'
>
> WARNING: CPU: 22 PID: 44011 at fs/iomap/iter.c:51
> CPU: 22 PID: 44011 Comm: fio Not tainted 6.8.0-rc3+ #1
> RIP: 0010:iomap_iter+0x32b/0x350
> Call Trace:
>  <TASK>
>  __iomap_dio_rw+0x1df/0x830
>  f2fs_file_read_iter+0x156/0x3d0 [f2fs]
>  aio_read+0x138/0x210
>  io_submit_one+0x188/0x8c0
>  __x64_sys_io_submit+0x8c/0x1a0
>  do_syscall_64+0x86/0x170
>  entry_SYSCALL_64_after_hwframe+0x6e/0x76
>
> Shinichiro Kawasaki helps to analyse this issue and proposes a potential
> fixing patch in [2].
>
> Quoted from reply of Shinichiro Kawasaki:
>
> "I confirmed that the trigger commit is dbf8e63f48af as Yi reported. I took a
> look in the commit, but it looks fine to me. So I thought the cause is not
> in the commit diff.
>
> I found the WARN is printed when the f2fs is set up with multiple devices,
> and read requests are mapped to the very first block of the second device in the
> direct read path. In this case, f2fs_map_blocks() and f2fs_map_blocks_cached()
> modify map->m_pblk as the physical block address from each block device. It
> becomes zero when it is mapped to the first block of the device. However,
> f2fs_iomap_begin() assumes that map->m_pblk is the physical block address of the
> whole f2fs, across the all block devices. It compares map->m_pblk against
> NULL_ADDR == 0, then go into the unexpected branch and sets the invalid
> iomap->length. The WARN catches the invalid iomap->length.
>
> This WARN is printed even for non-zoned block devices, by following steps.
>
>  - Create two (non-zoned) null_blk devices memory backed with 128MB size each:
>    nullb0 and nullb1.
>  # mkfs.f2fs /dev/nullb0 -c /dev/nullb1
>  # mount -t f2fs /dev/nullb0 "${mount_dir}"
>  # dd if=/dev/zero of="${mount_dir}/test.dat" bs=1M count=192
>  # dd if="${mount_dir}/test.dat" of=/dev/null bs=1M count=192 iflag=direct
>
> ..."
>
> So, the root cause of this issue is: when multi-devices feature is on,
> f2fs_map_blocks() may return zero blkaddr in non-primary device, which is
> a verified valid block address, however, f2fs_iomap_begin() treats it as
> an invalid block address, and then it triggers the warning in iomap
> framework code.
>
> Finally, as discussed, we decide to use a more simple and direct way that
> checking (map.m_flags & F2FS_MAP_MAPPED) condition instead of
> (map.m_pblk != NULL_ADDR) to fix this issue.
>
> Thanks a lot for the effort of Yi Zhang and Shinichiro Kawasaki on this
> issue.
>
> [1] https://lore.kernel.org/linux-f2fs-devel/CAHj4cs-kfojYC9i0G73PRkYzcxCTex=-vugRFeP40g_URGvnfQ@mail.gmail.com/
> [2] https://lore.kernel.org/linux-f2fs-devel/gngdj77k4picagsfdtiaa7gpgnup6fsgwzsltx6milmhegmjff@iax2n4wvrqye/
>
> Reported-by: Yi Zhang <yi.zhang@...hat.com>
> Closes: https://lore.kernel.org/linux-f2fs-devel/CAHj4cs-kfojYC9i0G73PRkYzcxCTex=-vugRFeP40g_URGvnfQ@mail.gmail.com/
> Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@....com>
> Fixes: 1517c1a7a445 ("f2fs: implement iomap operations")
> Fixes: 8d3c1fa3fa5e ("f2fs: don't rely on F2FS_MAP_* in f2fs_iomap_begin")
> Signed-off-by: Chao Yu <chao@...nel.org>
> ---
>  fs/f2fs/data.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index d9494b5fc7c1..5ef1874b572a 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -4185,7 +4185,7 @@ static int f2fs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>         if (WARN_ON_ONCE(map.m_pblk == COMPRESS_ADDR))
>                 return -EINVAL;
>
> -       if (map.m_pblk != NULL_ADDR) {
> +       if (map.m_flags & F2FS_MAP_MAPPED) {
>                 iomap->length = blks_to_bytes(inode, map.m_len);
>                 iomap->type = IOMAP_MAPPED;
>                 iomap->flags |= IOMAP_F_MERGED;
> --
> 2.40.1
>


-- 
Best Regards,
  Yi Zhang